Rihanna enjoys working out at 2am.

Fitness expert Ary Nunez revealed the Bajan beauty - who she has been working with for four years - is so dedicated to maintaining her trim figure and toned shape that she has the exercise guru on call at any time of the day in case she wants to train.

She said: "Working with an artist like Rihanna has different demands than most.

"We train when she's ready...even if we're on the road and it's 2am in the morning. I'm on call 24/7 with her."

During her workout sessions, the 23-year-old beauty tones her core muscles with an array of martial arts, dancing, and aerobic exercises - and Ary, who has worked with a number of celebrities, revealed the brunette singer exercises because she "loves it" rather than through necessity.

She added to Shape magazine: "Rihanna is so connected to her body. She used to work out because it was part of her responsibility, but now she works out because she loves it.

"We focus on The Core muscles, and we do a ton of repetitions."